The present invention relates to a flat transformer, and a power supply unit having a flat transformer. Further, the present invention relates to a flat transformer, and a portable information processing system and apparatus having a power supply unit, such as an office automation system and apparatus and an audio-visual system and apparatus.
In a conventional flat transformer, for example as disclosed in Japanese patent laid-open No. 42,907/1992, three foils having wide widths are insulated respectively and these three foils are contacted and wound. After winding these foils, the foils are cut down and thereby a square shape cross-section flat coil body is obtained.
A part of the coil body is used as a primary winding of the flat transformer and another part of the coil body is used as a secondary winding of the flat transformer, resulting in a flat transformer construction.
However, in the flat transformer obtained by the above stated conventional technique, since the coil body is disposed in a single plane, when the winding ratio between the primary winding and the secondary winding of the transformer exceeds more than 1:3, there appears a phenomenon in which the secondary winding does not contact the primary winding directly.
In the above mentioned case, the magnetic coupling between the primary winding and the secondary winding becomes extremely poor and thereby it causes a problem in which a required characteristic as a flat transformer can not be attained, because of a loss due to the poor electric power transmission.
Further, when a multi-output having more than three outputs is taken in a flat transformer, more than four conductors are required, resulting in a problem similar to the above stated problem.
Further, in the above described conventional transformer, the coil body is coated by an insulating member only at an inner side peripheral portion in which an adjacent coil body is contacted directly through the insulating member from a side direction. However, the coil body in the prior art is not coated by the insulating member at an upper face and a lower face thereof. Thereby, in the prior technique, it is impossible to overlap the coil bodies in both an upward direction and also a downward direction.
In a power supply unit in a personal apparatus, such as an office automation system and apparatus and an audio-visual system and apparatus, since a multi-output having various output voltages is required, there is a problem when the power supply unit is constituted with use of a flat transformer of the above stated conventional construction.
Further, in the flat transformer of the above stated conventional construction, since both a cross-section of a conductor of the primary winding and a cross-section of a conductor of the secondary winding are formed with a square shape, respectively, the electrostatic capacity between the primary winding and the secondary winding becomes large.
As a result, when the flat transformer in the prior art is used in a high frequency condition, in addition to the magnetic coupling characteristic of the flat transformer, a magnetic coupling between the primary winding and the secondary winding occurs due to the above electrostatic capacity and an oscillating phenomenon is generated between the electrostatic capacity and an inductance of an outside circuit such as a driving circuit.
Accordingly, in the conventional flat transformer, it is difficult to operate with the high frequency condition, and when it operates in a high frequency the loss increases and thereby it causes a problem in that it can not obtain a high efficiency in the flat transformer operation.